Programmable semiconductor devices include programmable read only memories (“PROMs”), programmable logic devices (“PLDs”), and programmable gate arrays. Programmable elements suitable for one or more of these device types include so-called “fuses” and “antifuses”.
A “fuse” is a structure which electrically couples a first terminal to a second terminal, but which, when programmed by passage of sufficient current between its terminals, electrically decouples the first terminal from the second terminal. A fuse typically consists of a conductive material which has a geometry that causes portions of the conductive fuse material to physically separate from each other to produce an open circuit when the fuse is heated to a given extent.
An “antifuse” is a structure, which when un-programmed, does not electrically couple its first and second terminals, but which, when programmed by applying sufficient voltage between the first and second terminals, permanently electrically connects the first and second terminals. One type of antifuse includes a highly resistive material between two terminals of conductive material, which when heated by an electric current, heats the materials and causes portions of the conductive material to extend into the resistive material and form a permanent conductive path. Another type of antifuse can be made of amorphous silicon which forms conductive polysilicon when heated. Fuses and antifuses have in common that their respective conductive state, once changed, cannot be reversed to again assume the initial state.
It would therefore be desirable to provide a connection between terminals, for example, of an integrated circuit, that can be programmed to switch between different conductive states in a reversible manner, i.e., that can operate reversibly both as fuses and as antifuses.